1. Field of the Invention
The present invention relates to a cooling air supply structure of a gas turbine that supplies cooling air to a turbine rotor blade and to a gas turbine.
2. Description of the Related Art
A gas turbine includes a compressor, a combustion chamber, and a turbine. The compressor compresses air taken in from an air intake, and thus the air is turned into high-temperature and high-pressure compressed air. The combustion chamber supplies fuel to the compressed air, thereby igniting the compressed air, and thus the compressed air is turned into high-temperature and high-pressure combustion gas. The turbine includes turbine stationary blades and turbine rotor blades within a casing thereof, in which the turbine stationary blades and the turbine rotor blades are alternately arranged. The turbine rotor blades are driven by the combustion gas supplied to an exhaust passage. Thus, the rotor connected to a power generator is rotationally driven. The combustion gas is converted into static pressure by a diffuser after driving the turbine, and is discharged into atmospheric air. In the gas turbine in the above configuration, a temperature of combustion gas acting on a plurality of turbine rotor blades reaches as high as 1500 degree centigrade, and the turbine rotor blades may be damaged because the turbine rotor blades are heated by the combustion gas. Therefore, the turbine rotor blades are cooled by supplying cooling air to each of turbine rotor blades.
Some of conventional gas turbines take out air from a compressor, and supply the air to the turbine rotor blades as cooling air. A cooling air supply structure of such conventional gas turbines includes an introducing passage extending in the radial direction of the rotor within each turbine stationary blade. The introducing passage is connected to an external pipe connected to a compressor in an exterior of the turbine stationary blades, and is connected to an air passage in an interior of the turbine stationary blades. The air passage faces in the direction of the rotor, and an outlet thereof is provided in the rotational direction of the rotor. A rotor cavity is provided on the rotor side of a space surrounded between a disk inner than the stationary blades in the radial direction of the rotor and the rotor. The rotor cavity is formed in such a way that an opening is formed thereon so that cooling air is introduced therethrough in the direction of the outer diameter of the rotor so that the rotor cavity is connected to a cooling passage provided within the turbine rotor blade behind the turbine stationary blade via a pressurizing passage extending in the radial direction of the rotor. The cooling air introduced to the introducing passage of the turbine stationary blade via the external pipe from the compressor is provided with swirl flow by being discharged so that the cooling air has a velocity component in the same direction of the rotation of the rotor, and is transmitted to the cavity so that relative velocity relative to the circumferential velocity of the rotor is reduced. Thus, the cooling air is supplied to the cooling passage via the pressurizing passage. A sealing member is provided between the inner circumference of the turbine stationary blade and the outer circumference of the rotor so that leakage of the cooling air into a casing is prevented (see, for example, Japanese Patent Application Publication No. 2002-517652 and Japanese Patent Application Laid-open No. 2000-310127).
In the cooling air supply structure of conventional gas turbines, the opening of the cavity is formed on the outer circumference of the rotor and the outlet of the air passage is provided on the inner circumference of the turbine stationary blade opposing the outer circumference of the rotor. In the configuration, a distance in the radial direction of the rotor between the outlet of the air passage and the central axis line of the rotor is larger than a distance in the radial direction of the rotor between a connecting opening of the pressurizing passage on the cavity and the central axis line of the rotor. Therefore, by rotation of the rotor, pressure is lower at the position of the connecting opening of the pressurizing passage than at the position of the outlet of the air passage. As a result, pressure acting on the seal member increases and the differential pressure across the seal member increases. Therefore, cooling air leaks into combustion gas, thereby reducing a thermal efficiency of the gas turbine.